Lately I have noticed that my starting speed is a little lazy and my headlights are not as bright.

So I took a closer look and measured the battery voltage while running the engine and get 12.5v - turning the lights on reduces this to 11.5v. All connections are good and the drive belt is tensioned correctly.

So is my alternator knackered or do I check anything else first?

What is battery voltage without engine running?

Are you able to measure voltage at the alternator ?(eliminates any volt drops in winging).


13.5 to 14.0 V is a good value when engine is running at about 2,000 rpm.

Check the charge lamp has not blown - this acts as a circuit to power the field coils.

Also check all connection are clean and tight from alternator and same for earth straps.

Could be your battery, try charging it with a battery charger and then disconnect the charger wait a few mins and check the resting voltage. You could also put an amp meter in the altinator curcuit to see what the charge rate is.

Check connections to alternator and earth strp
Charge the battery for a few hours.
Fit to car leave to settle, for 1/2 hour

Check Voltage
start engine run at 2-3000 rpm check voltage.

Turn head lights on -- run at 2-3000 rpm check voltage

Turn headlights off still at 2-3000 rpm watch for volatage spike.


All charging voltages should be in the range 13.4 to 14.9 volts.

Thanks for the input guys...

The battery was charged last night and I measured 12.5v this morning so I guess the battery is ok. Starting the engine doesn't really increase the voltage at all, although it does seem to match the demands of the ecu, coils, fuel pump etc - so it looks as if it is not pushing out enough juice to charge the battery (I would expect to see about 14v if all was ok)

The charge lamp in my case is an led (in the Evodash) and this behaves normally.

Turning the headlights on while running at 2000rpm reduces the battery reading to 11.5v and I can hear a low whine from the alternator (presumeably because its under load)

Methinks I'm going to be looking for an alternator now

Anyone know what vehicle this one is from?
Rescued attachment Alternator1.jpg

Looks like a Daihatsu/Nippon Denso

http://www.westfield-world.com/daihatsu_alternator.html

Yep a deson I think also fitted to Toyotas, our 4AGE has one.

Raz,

Does the LED have a resistor in parallel to mimic the normal light bulb? If not, I doubt whether the LED would pass enough current to activate the alternator coils.

An easy test would be to temporarily replace the existing LED indicator with a conventional bulb, and redo your voltage tests.

I suspect that the evodash would have this covered - but you never know.

HTH,
David

False alarm !!!

I just did a double check on all the connections, measuring voltages at various points and discovered that the engine earth strap was loose - and must have been that way for some time too!

Now getting 14v at the battery when running with the lights on and the starter motor now thinks it is on steroids! Whizzzzzz

Thanks for all the help guys

First rule of fault-finding - start with 'the bleedin' obvious', then 'simple' and, if all else fails, work your way up to 'difficult'!

Glad it was an easy one - cheap fix too...

Yep, I must have thought about the problem ar$e about face. The irony is that the earth strap is one of the first things I recommend looking at when charging problems are mentioned ......... duh